Agglomerating finely divided material



May 27, 1969 H. T. STIRLING AGGLOMERATING FINELY DIVIDED MATERIAL FiledMarch 22, 1966 FIG.

IN VEN TOR. 6641 040 77 577,94 nvo MSW F|G.30 FIG.3C

United States Patent 3,446,218 AGGLOMERATING FINELY DIVIDED MATERIALHarold T. Stirling, Pittsburgh, Pa., assignor to Stirling SinteringCompany, Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 22,1966, Ser. No. 536,348 Int. Cl. B01f 5/18, 9/02 US. Cl. 134-57 6 ClaimsABSTRACT OF THE DISCLOSURE This application relates to a method andapparatus for handling finely divided particles, and, more particularly,to a device capable of handling and wetting finely divided particleswithout forming clouds of dust.

During many industrial processes a substantial amount of material isobtained in the form of microscopically fine particles. Heretofore ithas been extremely diflicult to utilize these microfines. It has beenequally diflicult to dispose of the particles since they are formed inhuge quantities. Accordingly a great deal of finely rdivided ma terialhas been stockpiled. The cost of the real estate involved in thestockpiling operation has been in and of itself a long standing problemin many industries. Large quantities of this material would willingly besold at extremely low prices, or even given away, merely to reduce thesize and consequent cost of otherwise necessary stockpiling operations.

Recently, operations have been developed in which the finely divideddust-like particles have been pelletized hereby forming agglomerateswhich can be handled, and thus the finely divided particles areconverted into valuable and useful products. In order toformagglomerates or pellets from finely divided particulate material it isnecessary to wet the material to a predetermined moisture content suchas for example 5 to 20% moisture.

Heretofore the processes used to pelletize finely divided material'sinvolved adding such materials to a pelletizing drum or equivalentapparatus such as a cone pelletizer, disk pelletizer, or the like. Waterwas then added, in the pelletizer, to adjust the moisture content of thematerial. It has now been found that the capacity of a pelletizingapparatus can be significantly increased if water is added to the finelydivided dust-like particles to adjust the mixture to the desiredmoisture content before introducing the particles into the pelletizingapparatus. In this manner not only is the pelletizer simplified byelimination of water sprays, water pipes, controls, valves and othermiscellaneous equipment, but the necessity of moistening the particlesin the pelletizer is eliminated thereby allowing the full capacity ofthe pelletizer to be used for pelletizing. This results in a significantincrease in output. The average residence time of the particles in thepelletizer is also decreased when the particles in the pelletizer arewet when they enter.

It is an object of this invention to provide apparatus for handlingextremely finely divided material.

Another object of this invention is to provide means for handling andtreating finely divided material to produce particles that have notendency to form dust clouds.

A further object of this invention is to provide a method and apparatusfor Wetting finely divided particles which would normally resist suchwetting due to their finely divided nature.

The invention resides in certain novlel features of process andapparatus and in the combination and arrangement of steps and of theparts of the apparatus in which the invention is embodied; land theadvantages of the invention will be apparent to those skilled in the artto which the invention pertains from the following description of theembodiments thereof described with reference to the accompanyingdrawings in which:

FIGURE 1 is an elevational view of the apparatus shown partially incross section,

FIGURE 2 is a plan view of the wetting drum of the invention,

FIGURE 3 is a vertical cross sectional view of the wetting drum, and

FIGURES 3n, 3b, and 3c are vertical, cross-sectional views showingalternate embodiments of the incoming feed duct and water inlet meanstaken on lines A-A of FIGURE 3.

Referring now to the drawings there is provided a hopper '10 which isfilled from any suitable source with finely divided dust-like particles.Hopper 10 is mounted on means to assist the flow of particles from thehopper generally indicated by reference numeral '12, which in turn ismounted on inlet means 14 of screw conveyor 16. Means 12 is provided toensure positive flow of the finely divided material from hopper 10 intoscrew conveyor 16 in any suitable way such as by vibrating the materialin the hopper. For this purpose in the embodiment depicted vibratingcone 18 is mounted in casing 20 of means 12 and extends into hopper 10.

Casing 20 is joined to the hopper 10 and to inlet '14 of screw conveyor16 by flexible means 22, 24 adapted to isolate the vibrations of flowassisting means 12 from both the hopper 10 and the screw conveyor 16. Tothis end connecting means 22, 24 may comprise flexible rubber sealingmeans to prevent the discharge of any finely divided material into theatmosphere. A motor 26 or other suitable device is mounted on casing 20to vibrate cone 18. The use of flow assisting means 12 with itsvibrating cone 18 ensures continuous flow of the feed material byeliminating bridging of the fines which otherwise would normally takeplace when a hopper or bin is filled with finely divided material.Similar equivalent apparatus can be substituted for the above describedmeans 12 but advantageously some device should be used to ensure acontinuous flow of the feed material.

The material from hopper 10 is fed into doubledlight screw conveyor 16which is one-half pitch for the first half of the length and thenstandard pitch for the remainder. The configuration of the screwoperates to control the rate of feed and eliminate gross variations inthe rate of feed of the finely divided particles.

In this manner flooding of aerated materials is prevented and the effectof any surges of material from the bin are minimized. The one-half pitchfor the first half of the conveyor can suitably be obtained by using adouble flight of standard pitch for the first half of the conveyor and asingle flight of standard pitch for the remainder. Screw conveyor 16 isprovided with variable speed drive means 28 which is operated by a motor30 or other prime mover. The speed at which the screw conveyor isactuated is controlled by speed controller 31 in accordance with acontrol system described hereinbelow.

Screw conveyor 16 is provided with two valved outlets 32, 34. Outlet 32transfers the material into the next stage of the feed mechanism to thewetting apparatus. If it is desired, however, to bypass the wettingsystem valve 33 in conduit 32 is closed and valve 35 in conduit 34opened thereby allowing the material in the screw conveyor 16 to bypassthe system, and be delivered to other processing equipment. Materialdischarged by screw conveyor 16 through outlet 32 is deposited ontocontinuous conveyor belt means 36 disposed in a dust tight housing 38.Continuous conveyor 36 is driven by any suitable variable speed drivemeans (not shown).

Referring now to FIGURES 2 and 3 of the drawings, dust wetting drum 40comprises a rotatable drum having a generally frusto-conical side wall41. The smaller end 42 of drum 40 opens upwardly to receive feedmaterial, and the larger end 44 forms the base and back wall of thetruncated conical member. The open end 42 of drum 40 is provided with alip 46 to direct the material as it is discharged from the wetting drumonto suitable removal means such as conveyor 55.

Incoming feed is introduced through the small open end 42 of wettingdrum 40 through a chute member 50 having its discharge end positionedsubstantially below the level of material in the wetting drum wherebythe incoming dust-like material is fed into the drum below said level ofmaterial. Water is sprayed into drum 40 through conduit 45. The incomingdust becomes moist ened because the material in the wetting drum intowhich the incoming microfines are fed has previously been wetted and theparticles therefore have wet, glossy surfaces. Thus the particles indrum 40 either individually or in lumps or agglomerates, are wet withsurface moisture. As this wet material rolls past the inlet chute 50 forthe dust-like material, the incoming feed attaches to the moistenedsurfaces almost in the same manner as a magnet will pick up iron powder.Because of this ability of the already moistened material in drum 40 topick up the incoming feed, a temporary unexpected shutoif of water willnot cause a cloud of dust as would be present in a pug mill or the like,and furthermore the moisture content of the material discharged from thewetting drum will always be maintained uniform.

Wetting of hot or cold microfines such as precipitator dust or othervery fine material has heretofore been approached with the idea ofbreaking down the surface tension of the particles with a fine spray ofwater. This requires a relatively great amount of time i.e., in excessof one minute. By the present system, once the first surge of materialis wet, the revolving fines and/or small seed pellets with surfacemoisture present on the exposed surface thereof begin to gently rollunder and around the entry chute. This depth of flowing or rollingmaterial buries the entire entry chute so that the incoming fine dustcannot escape. The continuous rolling action causes the discharge end ofthe incoming feed duct 50 to be sealed by the flow of wet rollingparticles with glossy surfaces from the moisture present thereon. Thedry incoming dust is then picked up on the wet sticky surfaces of thegently rolling particles.

Water sprays continuously discharge onto the rolling particles in orderto keep them wet so that the surface area will maintain its layer ofsticky moisture. Once a wet particle of agglomerate has gone under theincoming feed duct 50 and picked up additional dry dust on its wetsurface a portion of its surface moisture is absorbed into thepreviously dry dust now adhering thereto. The moissurface of theinitially wet particles adhering to the surface of the intially wetparticle eliminates the water repellency that dry dust particlesnormally possess. It then becomes possible to further wet the newparticle (agglomerate) by spraying the surface of the revolving materialwith water. This causes the surface of the new particle to become wetand glossy and capable of picking up additional dry dust when it passesunder the incoming feed duct. The above described cycle is repeated manytimes on each particle until it is discharged from the wetting drum. Thetreated material discharged from the wetting drum had a very uniformmoisture content. The particles are, of course, larger than theextremely fine particles originally fed thereto and therefore have no 4tendency to form clouds of dust, are easily handled, and may be furtherprocessed in many ways.

The water added to drum 40 can be added either within dust inlet 50 ordirectly onto the surface of material in the wetting drum and, ifdesired, in both locations. To this end water inlet conduit 45 may beprovided with two branch conduits 47, 40 (FIG. 3a) each fitted with aspray nozzle. Spray nozzle 51 on branch 47 will desirably form a fine,mistlike curtain of water through which the incoming dust will pass. Inthis manner the spray helps both to wet the incoming material bystarting to break down the surface tension and also to keep the alreadymoist surfaces wet. The fine spray inside chute 50 will also help inkeeping the incoming dust from blowing back up the entry chute. At leastone one spray nozzle 53 on conduit branch 49 is advantageously adaptedto direct a fine spray over a large portion of the surface of materialin drum 40. In FIGURE 1, for example, there is shown a modificationwherein two spray nozzles 53 are used.

While the embodiment of the invention shown in FIG- URES 2 and 3autilizes a plurality of sprays it may be desirable to use only a singlespray whereupon the spray may be directed only within chute 50 as shownin FIG- URE 3b or the spray may be discharged solely onto t e surface ofthe material in drum 40 as shown in FIGURE 30. In all embodiments of theinvention, even where the sole spray is located within chute 50 the dustis primarily wetted because the rolling wet material picks up the drydust as the material with a wet, glossy, sticky surface passes the entrychute 50.

In order to control the amount of wetting, a proportioning system shouldbe used in conjunction with the wetting drum. The automatic controlsystem of the invention comprises a weight detector 60 of known designadapted, in combination with computer 62, to continuously measure andderive a signal having a magnitude proportional to the weight ofmaterial on conveyor 36. Computer 62 is set to deliver a predeterminedrate of feed. A constant feed rate is maintained by varying throughspeed controller 31, the speed of screw conveyor 16 in accordance withvariations in the detected weight of material on conveyor 36. Waterproportioning means comprising flow recorder controller 64 isoperatively associated with computer 62 and adapted to adjust the rateof addition of water into drum 40 upon variations in the amount of drymaterial fed thereto as determined by fluctuations in the detectedweight of material on conveyor 36.

In one embodiment of the invention the chute 50 is shaped in such manner(FIG. 1) that a maximum of surface is available for contact between theflowing wet particles and the incoming dry dust. Accordingly, the openend of chute 50 is provided with a horizontally extending bottom openingand a second open portion extending generally in the same direction asthe bottom 44 of drum 40. To the same end the horizontal cross sectionalarea of the chute 50 may be larger at the bottom than at the topthereof.

The entire feed system is enclosed in a dust tight housing from the bin10 to the open end 42 of wetting drum 40. The system described therebyeliminates air pollution. No dust rises from the open mouth 42 of thedrum because the surface particles in the drum are sufficiently wet toensure that none become airborne. The effectiveness of the surfacemoisture is enhanced due to the depth at which the incoming feed isadded.

The drum 40 is adjustably set at an incline of between about 20 and 30degrees upwards from the horizontal to provide the desired degree ofwetting. The bottom 44 of the wetting drum is reinforced by structuralmeans 61. The drum 40 is rotated by motor 63- through reducer 65 andstub shaft 67.

As set forth above, the wetted dust can be further processed and isespecially useful as feed material for a pelletizer. For this use theprewet particles increase the I claim:

1. Apparatus for the handling and treatment of dry dust-like materialcomprising, a hopper for said material, conveyor means for receivingsaid material frfom said hopper, a dust-tight housing for said conveyormeans, downwardly extending chute means for receiving said material fromsaid conveyor means and for delivering said material into a drum forforming a bed of material therein, a drum adapted to receive saidmaterial from said chute, and means to spray water onto the material insaid drum, said chute extending into said drum and into said bed ofmaterial, at a point below the normal surface level of material in saiddrum whereby the mouth of said chute is sealed by the material alreadyin said drum and further comprising means to rotate said wetting drum tocause the bed of material in said drum to continuously flow past saidmouth of said chute whereby incoming solid particles are continuallypicked up on the surfaces of the wet particles in the interior of thebed of material in said wetting drum.

2. The apparatus of claim 1 wherein said conveyor means comprises, ascrew conveyor adapted to receive said material from said hopper, and acontinuous belt conveyor adapted to receive material from said screwconveyor and to transfer said material to said chute means.

3. Apparatus as defined in claim 2 wherein said screw conveyor means isdivided into two sections, a first section adjacent the inlet thereofhaving flights, the pitch of said flights being about one-half the pitchof the flights in the second section adjacent the outlet thereof,wherein means are provided contiguous to the connecting means betweensaid hopper and said screw conveyor for vibrating the dust in saidhopper to ensure substantially continuous flow of said dust from saidhopper into said screw conveyor, and further comprising bypass means topermit said material to bypass said wetting drum.

4. The apparatus of claim 1 in which the downwardly extending chutemeans extends through an opening in the drum and downwardly below thelowest level of the opening in the drum.

5. The apparatus of claim 4 and further comprising, means to detect theamount of feed material" added to said drum'member, and means toautomatically adjust the rate of addition of water in response tochanges in said detected amount.

6. The apparatus of claim 4 wherein said means to add water to said drummember comprises means to spray water onto the surface of the bed ofmaterial in said drum, and said means to feed material into said drumcomprises a chute extending below the surface of said bed of material.

References Cited UNITED STATES PATENTS 2,586,818 2/1952 Harms 23--3132,834,044 5/ 1958 Antonsin 233 14 3,092,489 6/1963 Smith 23-3 132,297,300 9/1942 Hardesty 233 13 2,304,382 12/1942 Shoeld 233132,436,771 2/ 1948 Hood 23-3 13 2,860,598 11/1958 Loesche 233 132,961,411 11/1960 Klugh 23-313 FOREIGN PATENTS 1,156,013 10/1963Germany. 612,359 l/1961 Canada.

NORMAN YUDKOFF, Primary Examiner.

US. Cl. X.R.

